1. Field of the Invention
The present invention relates to conversion of frequencies. More particularly, the present invention relates to converting and coupling shortwave radio signals to a standard AM radio.
2. Description of the Prior Art
It has been known in the art to convert a shortwave signal into an aM signal for reception on a standard AM radio. The typically this requires a converter to be connected to the antenna or input of the AM radio. The converter is electrically connected to a shortwave antenna on an input end and an antenna or input of the AM radio on the output end. The converter changes the received signals in the shortwave bands into AM signals which are received by the AM radio. A significant drawback to this arrangement is that the AM radio tuner is used to select the frequency of the desired shortwave signal. However, the scale of the tuning dial on the AM radio is matched to AM frequencies. Thus the user cannot tune to a preselected frequency easily. There is a need for a converter which permits the user to select an aM frequency, free from interference, to which the incoming shortwave frequencies are changed. Further the converter needs to have the capability to tune to selected shortwave frequencies.
Numerous innovations for Shortwave A. M. Broadcast Converter have been provided in the prior art that are described as follows. Even though these innovations may be suitable for the specific individual purposes to which they address, they differ from the present invention as hereinafter contrasted.
In U.S. Pat. No. 4,490,837, titled AM Stereo to FM Stereo Converter, invented by Gregory J. Buchwald, a converter is coupled between the antennan and the RF stage of an FM stereophonic receiver to convert received AM stereo signals into FM stereo signals, and decoded into two stereo signals. These signals are ten encoded into a broadcast-type FM stereophonic signal which is coupled into the front end of an FM stereo receiver.
In U.S. Pat. No. 4,112,377, titled C. B. Converter, invented by James L. Tanner and Bruno A. Rist a converter is disclosed for converting 23-channel citizens band to provide citizens band reception through a standard radio, preferably an automotive radio. The circuit is comprised of an RF amplifier and self-oscillating converter which is switched into the antenna connections of an automobile radio. Conventional auto antenna connectors facilitate easy installation. A push-button switch connects the citizens band converter into the line connecting the antenna with the radio. The pish-button switch also grounds the converter output when switched to standard radio to prevent interference with standard radio reception.
In U.S. Pat. No. 4,001,729, titled FM to AM Converter, invented by Howard L. Weinberger, an FM to AM converter which utilizes a source of unmodulated radio frequency energy, two mixers, and a filter to convert an FM signal to an AM signal. The incoming FM signal is mixed with the unmodulated RF energy. The mixed signal is then passed through a filter to generate AM on the mixed signal together with the FM. The amplitude modulated mixed signal is then mixed with the original FM signal to trip off the FM from the amplitude modulated mixed signal thereby generating an AM signal.
In U.S. Pat. No. 3,983,487, titled FM-AM Converter, invented by Masaharu Ohno, an FM-AM converter in which the FM signal is applied to a slope filter in a transmission system. The resulting amplitude modulated FM signal is applied to a circuit that delivers a control signal corresponding to the mean value of the amplitude modulated FM signal and uses this control signal to control either the gain of the FM signal applied to the slope filter or the frequency response of the slope filter so that the amplitude of the amplitude modulated FM signal will have a predetermined mean value.
Numerous innovations for Shortwave A. M. Broadcast Converter have been provided in the prior art that are adapted to be used. Even though these innovations may be suitable for the specific individual purposes to which they address, they would not be suitable for the purposes of the present invention as heretofore described.